1. Field of the Invention
The present invention is related to a method or apparatus providing a multicast transmission in a communications network. More particularly, the present invention is related to a method or apparatus controlling the power of a multicast transmission in a wireless communications network.
2. Discussion of the Related Art
3GPP TS 23.041 V4.1.0 (2001-06) describes a Cell Broadcast Service (CBS) for a wireless communications network according to the specifications of the 3rd Generation Partnership Project (www.3GPP.org) which is similar to Teletext service offered on television, in that it permits a number of general messages to be broadcast and received by all receivers within a particular region. These CBS messages are broadcast to defined geographical coverage areas also called cell broadcast areas. A cell broadcast area may comprises one or more cells, or may comprise the entire cellular network. Individual CBS messages are assigned their own cell broadcast area by a mutual agreement between the information provider and the network operator. They may originate from a number of different Cell Broadcast Entities (CBEs), which are connected to a Cell Broadcast Center (CBC). CBS messages are then sent from the CBC to the cells via a radio access network in accordance with the CBS's coverage requirements.
CBS has the disadvantage that the messages are broadcast indiscriminately to all receivers within the geographical coverage area. It cannot identify different UEs for comprising a multicast group or make evaluations between different cells (e.g., the number of UEs in a cell, etc, etc.) or between different sessions (e.g. delay requirements for transmission, session priority, etc.)
3GPP TS 22.146 V2.0.0 (2001-09) describes, at a high level, the requirements desired for an envisioned multicast service. Unlike CBS, the multicast service uses common network resources to provide data communications only to a restricted group of people in one or more cells of the network who previously indicated their interest to receive the multicast service.
The intent is to enhance the current capabilities of the Universal Terrestrial Radio Access Network (UTRAN) and the Core Network (CN) to make them become capable of providing the envisioned multicast service. For example, the core network which knows only the Location/Routing area level of the UEs of a plurality of service subscribers will forward the data to be multicast to the UTRAN. The UTRAN, which knows the various cell locations of the UEs, in turn transmits the data to each of the UEs in a cell through one common physical channel on the radio interface. The transmissions of the multicast data in the various cells may be simultaneous or may be scheduled. Possible physical channels could be, for example, the Secondary Common Control Physical Channel (SCCPCH) which is currently used to transmit data of the transport channel and the Fast Access Channel (FACH) which can transmit CBS data as well as other types of data.
The power level used for the transmission of a common physical channel (for example, open loop power control) is typically defined based on cell structure and the conditions of the air interface (i.e., as defined by the radio access network) without checking the conditions in the cell from the UE point of view or the locations of the UEs. It is typically fixed and set high enough so that the UE furthest from the base station and almost at the border of the cell is able to receive the transmission. This has the disadvantage that the power level is unnecessarily high for most of the UEs. From the air interface point of view, it also results in interference which could be avoided if the radio access network had information about authorised UEs in the cell.
Location information at least from URA (UTRAN Registration Area) level can usually only be fetched from a Radio Network Controller (RNC) if the authorized UEs and the UEs are in a Radio Resource Controller (RRC) connected state. However, it is more than likely that the most of the UEs are in IDLE mode and have no RRC connection. Therefore their precise location is unknown to the radio access network and the power level of the multicast data transmission cannot be controlled accordingly. In order to transmit the multicast data more efficiently, the radio access network should know the condition in the cell from the UE point of view and the locations of the authorized UEs, such as whether there are any UEs in a cell upon activation of the multicast data transmission, and adaptively control the power level accordingly before transmitting the data. Thus, there is a need for a system or apparatus for allowing the RNC to keep a record of the location of the UEs in the cells even though they are in the IDLE mode.